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Posted: December 13, 2020
Dam concrete repair necessary for future performance
By Don O’Connor, P.E., chief of construction and planning
MCD is committed to keeping the dams and other flood protection structures operating safely and properly for your protection. To that end, we are nearing completion on a $2.61 million project to improve concrete at Lockington Dam. Over the last 13 months, MCD’s contractor has removed and rebuilt up to 15 feet of concrete on top of the dam’s upstream and downstream right bank wall as well as repaired concrete on the face of the wall.
This project was necessary. While there was little danger that the wall might fail during a high-water event, there was significant deterioration. Had we waited another 10 or 20 years, the extent of damage would have been more severe and much more expensive to repair. Addressing this rehabilitation in a timely manner is financially responsible. And it could be dangerous if put off for too long.
Freeze/thaw cycles damaged the concrete
Over the decades, water has seeped into the walls through joints and cracks. That water has been a destructive force because of the innumerable freeze/thaw cycles that caused the water to expand and turn into ice. This caused extensive damage to the outer surface of the concrete walls.
The last significant concrete repair at Lockington and the other four flood protection dams took place in the 1970s with a material called shotcrete. The shotcrete repaired the previous surface deterioration, but the freeze/thaw cycles eventually damaged the material and caused some of it to detach from the walls. The Lockington Dam shotcrete was beyond its useful life and needed to be replaced.
With the current repair, MCD’s contractor also installed an underground drain system behind the concrete wall to keep rainwater and snowmelt from seeping into the wall joints. The drains are designed to help prevent the damage caused by the freeze/thaw cycles.
More work to come
Concrete repair at Lockington Dam is the first of many concrete projects to come. MCD is planning additional work at Lockington Dam along the left wall. Each of the dams will likely need similar work. Studies are planned for the other four dams to determine the extent of repairs needed and to prioritize work for future projects.
The right-wall project at Lockington was the culmination of years of work and monitoring. MCD frequently inspects its dams. Those inspections began to show a need for more detailed investigation/structural analysis. That analysis helped MCD understand the scope of work needed at the dam, leading to the design and construction.
These kinds of projects are years in the making. But it’s important we take the time to follow a logical process, determine the need, and complete it as cost-effectively as possible.
Don O’Connor is MCD’s chief of construction and planning. He joined MCD in 2018 and is a licensed professional engineer.